Vinyl chloride-containing polymers having a high stability against thermal decomposition



Patented Sept. 13, 1949 VINYL CHLORIDE-CONTAINING POL HAVING A YMEIRS IIIGII STABILITY AGAINST THERMAL DECOMPOSITION Thurman V. Williams, Niagara Falls, N. I, as-

slgnor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application March 11, 1941,

Serial No. 734.000

8 Claims. (Cl. 260-923) 1 This invention relates to the production of vinyl chloride-containing polymers, and more particularly it relates to a new and improved process of the production of such polymers having a highly desirable stability against thermal decomposition. This invention is particularly applicable to vinyl chloride-containing ploymers containing at least 50%, by weight, vinyl chloride (CH2=CHCL) units, 1. e., polymers obtained by the polymerization solely of vinyl chloride (commonly referred to as polyvinyl chloride) and polymers obtained by the conjoint polymerization of vinyl chloride and another polymerizable substance and in which the vinyl chloride constitutes 50%, by weight, of the resulting copoiymer.

This application is a continuation-in-part of my copending application Serial No. 563,304 filed November 13, 1944, now abandoned.

Vinyl chloride-containing polymers containing at least 50% by weight of vinyl chloride units are subject to thermal decomposition when heat processed above the softening point thereof in the iormation of various articles, for example, when heat molded, injection molded, heat calendered and the like. These polymers are particularly subject to thermal decomposition, as evidenced by discoloration, when they contain even trace amounts of certain metal salts, particularly iron salts.

In order to isolate vinyl chloride-containing polymers from aqueous dispersions thereof, several methods have proven workable and are known in the art. One method of isolation involves spray-drying oi the dispersion. In this process, the aqueous polymer dispersion is sprayed into a jet of combustion gases. The temperature of these gases is such that the water contained in the dispersion is rapidly vaporized to superheated steam. The dry polymer is then separated from the gaseous phase in a so-calied cyclone separator. It will be evident that this process results in the removal of none of the nonvolatile impurities in the dispersion. Another method of isolation involves drum drying. By this process, the aqueous dispersion is run into the gap between two heated rolls. The temperature and speed of the rolls are adjusted so that near the end of the revolution the water has been volatilized. The solids are scraped of! the roll at this point. As in the spray-drying process, none 01' the impurities are removed by drum drying Where it is desirable to obtain a polymer materially free dispersing agent, water-soluble chloride-containing polymer is isolated by coagulation with an electrolyte. Numerous acid and salt electrolytes have been used for this purpose. The use of an acid, for example, sulfuric acid, as the coagulant is objectionable in that it results in the production of a soft sticky mass which is very dimcult to reslurry with added water. It is, therefore, preferred to use, as the coagulant, a watersoluble metal salt electrolyte which will not form a water-insoluble precipitate with acids which are present in the dispersion.

The use of such water-soluble metal salt electrolytes, as coaguiants, will under normal circumstances prevent removal oi objectionable quantities of iron, manganese, nickel and copper salt impurities which may be present in the resin dispersion. The presence of iron, manganese, nickel or copper salt impurities in the final resin product will enhance the thermal instability oi the resin and they are therefore, highly objectionable. Furthermore, when insoluble hydroxide-forming, water-soluble metal salts, for example, aluminum salts, are used as the coagulants, insoluble hydroxides will be formed in the coagulated mass. Although aluminum hydroxide may not add to the inherent thermal instability of the resin, it is generally incompatible with the fused resin and results in haze in unpigmented resin formulations.

It is an object of the present invention to provide a new and improved process for the production of vinyl chloride-containing polymers containing at least 50% by weight vinyl chloride units.

It is another object of this invention to produce vinyl chloride-containing polymers containing at least 50% by weight vinyl chloride units which will have an improved stability against thermal decomposition.

It is still another object of this invention to provide a process for treating an aqueous dispersion of a vinyl chloride-containing polymer which will solubllize inorganic impurities therein and permit their removal by washing with water.

It is another object of this invention to provide a process for the production of vinyl chloridecontaining resins from an aqueous dispersion thereof, which process will readily remove iron, manganese, nickel or copper, or aluminum impurities which may otherwise remain in the resin product.

Other objects of the invention will appear hereinafter.

The objects of the invention may be accomsalts, etc., the aqueous dispersion oi the vinyl p s ed. i e b adding o an queous dission ota vinyl chloride-containing resin conining at least 50% by weight vinyl chloride units, suflicient water-soluble acid to reduce the pH value of the dispersion to such a level that inorganic impurities will be in solution and remain in solution during subsequent coagulation, filtration and washing steps. The polymer is then coagulated from the dispersion by means of a water-soluble metal salt which will not form a water-insoluble salt with any acid present in the polymer dispersion, and is then filtered. washed, neutralized, if necessary, and dried.

It has now been found that lit a watgreasolgible acid, preferably a mineral aci is ad an aqueous dispersion of a vinyl chloride-containing polymer containing at least 50% by weight of vinyl chloride units and containing a dispersing agent which is not materially ailected by said added acid to demulsii'r the dispersion in an amount insuillcient to coagulate the polymer but suillcient to reduce the pH value below 2, deleterious metal salts contained in the will remain in solution after coagulation with said water-soluble metal salt electrolyte. The

polymer can. after coagulation. be washed with water to remove objectionable salts contained in the coagulated polymer. Furthermore. y this process, the coagulated polymer will have a granular form which is readily re-dispersed by addition of water.

As above stated, the aqueous vinyl chloridecontaining polymer dispersion should contain, as the agent therein, a agent which is not materially affected by the step of acidification to demulsify the dispersion, i. e., the dispersing agent must be stable against decomposition at a pH below 2. As examples of such dispersing agents, the following may be named: sodiumalkylsulfatescontainlng'ltolllcarbon atoms, for example sodium lauryl sulfate, sodium cetyl sulfate or sodium myristyi sulfate: sodium alkyl suli'onates. i. e.. compounds having the general formula Ji -0N.

in which R designates an alkyl radical having between 12 and is carbon atoms.

The acid used in lowering the pH value of the 50 aqueous polymer dispersion should. oi course, be sufliciently strong to readily lower the pH value below 2. The following are examples oi acids which may be used for this P rpose: hydrochloric acid, sulfuric acid, acetic acid, and para-toluene suli'onic acid. Preferablv. hy rochloric or sulturic acid is used in the lowering of the pH value.

Aqueous dispersions of vinyl chlorlde-cwtaining polymers are usually prepared by methods which will produce dispersions having a pH value of between about 2.5 to 4.0. with such dispersions the acid can be added to lower the pH value to around zero without coagulating the polymer. However, in the case of aqueous polymer dispersions having a high pH, for example, 6 to 10, the pH value may only be lowered to about 1.0 or even 1.5 to avoid precipitating the polymer.

As the water-soluble metal salt electrolyte, any metal salt may be used which will not form an insoluble salt with acid which is present in the dispersion. For example, aluminum chloride. aluminum sulfate, sodium or potassium chloride. or sodium or potassium acetate may be used for this purpose. Water-soluble aluminum salts are preferred. When the dispersion contains suliate ions.barlumorcalciumsaltscannotbeusedsince they would form insoluble salts in the mass.

The invention is applicable to vinyl chloride polymers consisting entirely oi vinyl chloride units, i. e., polyvinyl chloride, or it is applicable to and inter-polymers in which at least 50% of the polymer consists 01' vinyl chloride units and the remainder consists of other polymer units. As examples of copolymers which will be stabilized in accordance with the present invention, the following may be named: vinyl. chloridefumaric ester copolymers, vinyl chloride-vinyl acetate copoiymers. vinyl chloride-vinylidene chloride copolymers, vinyl chloride-vinyl cyanide vinyl chloride-acrylic ester copolymers and vinyl chloride-methacrylic ester copolymers. Preferably, the polymers to be treated in accordance with this invention are those prepared from monomers which contain only oneethylenic double bond. I

The following examples, illustrate, in specific detail, certain preferred processes for carrying out the process of the present invehtlon, it being understood thaat the invention is not limited to the details set forth in the examples.

Example I Aqueous dispersion of a 95-5 vinyl chloridediethyl fumarate copolymer of solids pH=2.9 containing as the dis agent, 1% by weight of sodium lauryl sulfate of the copolymer .g.. 500

Aqueous hydrochloric acid solution suilicient to reduce the pH of the polymer diapersionto 2.0-1.0 N 10 Aluminum sulfate solution. 1 N. aqueous ammonium hydroxide per cent.- 10

The polymer dispersion was prepared by emulsion polymerization of the mixed monomers. The pH of the resulting dispersion was 2.0. The dilute hydrochloric acid was added slowly to the dispersion with agitation. When the pH had reached 1.4, 25 cc. of the aluminum sulfate was added. The dispersion immediately set up to a friable mass that appeared to be nearly dry. Bufllcient water was added to result in a workable slurry, and the solids were separated oil and washed well with water. They were then reslurried in dilute ammonium hydroxide, filtered out. again thoroughly washed with water and dried at atmospheric pressure and 65 C. for five hours. Approximately 147 g. dry, white resin powder was obtained. When this powder was molded for 2 minutes at 165 C. and 1000 lbs. per pressure, a very light amber sheet re- Example I! Asecondsampleoi the polymerof Example I was coagulated exactly according to the scheme outlined in that example except that the pH was not lowered. A molding oi the isolated resin was light brown, with green blotches,

when pressed for 2 minutes at 165 C. and 1000 lbs. per sq. in. pressure.

Example [I] v A third sample of the polymer dispersion of Example I was coagulated as outlined in that example except that no hydrochloric acid was added; instead the pH was raised to 8.0 with dilute ammonium hydroxide prior to addition of aluminum sulfate. A melding of the resin isolated bythlsprocedure wasanuneven brown color loonanaveragetothefleiligevarnish 8 color standard No. 15. This sheet was not quite clear.

Example IV Aqueous dispersion oi polyvinyl chloride,

36% solids pH=2.'7 containing as ,a dispersing agent, 0.75% by weight of sodium lauryl sulfate 01' the polymer -g 500 Aqueous hydrochloric acid solution suillcient to reduce the pH of the polymer dispersion to 2.0-1.0 N 5 Aluminum sulfate solution per cent Aqueous ammonium hydroxide N 1 This dispersion was coagulated according to the scheme outlined in Example I. A sheet prepared by pressing the powder for two minutes at 165 C. and 1000 lbs. per sq. in. pressure was clear amber. As in Examples II and III, coagulations carried out at pH=2."l and 8 respectively yielded resins which were progressively less stable to thermal decomposition.

Example V Aqueous dispersion of a 95-5 vinyl chloride methyl acrylate interpolymer. Solids content; 20%, pH: 20.75 containing as a dispersing agent, sodium white oil sulfonate g Aqueous hydrochloric acid solution sufllcient to reduce the pH of the dispersion to 2.0-1.0 N 5 When isolated according to the scheme outlined in Example I, this resin yielded a sparkingly clear film by pressing at 165 C. and 1000 lbs. per sq. in. for 2 minutes. It was light amber in color. The resin resulting from basic coagulation as in Example III yielded a brown film with greenish blotches when pressed at 165 C. and 1000 per sq. in. in for 2 minutes.

Since it is obvious that many changes and modifications can be made in the above described details without departing from the nature and. spirit of the invention, it is to be understood that the invention is not to be limited to said details except as set forth in the appended claims.

What is claimed is:

1. The process of producing a vinyl chloridecontaining polymer having a high stability against thermal decomposition which comprises adding to an aqueous dispersion of a vinyl chloride-containing polymer taken irom the group consisting of polyvinyl chloride, vinyl chlorideiumaric ester copolymers, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidenechloride copolymers, vinyl chloride-vinyl cyanide copolymers, vinyl chloride-acrylic ester copolymers and vinyl chloride-methacrylic ester copolymers, said polymer containing at least 50%, by weight, vinyl chloride units and containing as the dispersing means therein a dispersing agent which is stable at a pH below 2.0, suilicient watersoluble acid taken from the group consisting of hydrochloric acid, sulfuric acid, acetic acid, and para-toluene sulfonic acid to lower the pH value of the dispersion to less than 2.0 but. insuflicient to coagulate the polymer from the dispersion, adding to said dispersion, in suilicient amount to coagulate said polymer, a water-soluble metal salt which will not form an insoluble salt with acid present in said dispersion, and washing said coagulated polymer.

2. The process as defined in claim 1 in which the vinyl chloride-containing polymer is polyvinyl chloride.

8. The process of producing a vinyl chloridecontaining polymer having a high stability against thermal decomposition which comprises adding to an aqueous dispersion of a vinyl chloride-containing polymer taken from the group consisting of polyvinyl chloride, vinyl chloridefumaric ester copolymers, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-vinyl cyanide copolymers, vinyl chloride-acrylic ester copolymers, and vinyl chloride-methacryiic ester copolymers, said polymer containing at least 50%, by weight, vinyl chloride units and containing as the dispersing means therein a dispersing agent which is stable at a pH below 2.0, suflicient sulfuric acid to lower the pH value of the dispersion to less than 2.0 but insufllcient to coagulate the polymer from the dispersion, adding to said dispersion, in suillcient amount to coagulate said polymer, a water-soluble metal salt which will not form an insoluble salt with acid present in said dispersion, and washing said coagulated polymer with water.

4. The process of producing a vinyl chloridecontaining polymer having a high stability against thermal decomposition which comprises adding to an aqueous dispersion of a vinyl chloride-containing polymer taken from the group consisting of polyvinyl chloride, vinyl chloridefumaric ester copolymers, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-vinyl cyanide copolymers, vinyl chloride-acrylic ester copolymers, and vinyl chloride-methacrylic ester copolymers, said polymer containing at least 50%, by weight, vinyl chloride units and containing as the dispersing means therein a dispersing agent which is stable at a pH below 2.0, suillcient hydrochloric acid to lower the pH value of the dispersion to less than 2.0 but insuil'lcient to coagulate the polymer from the dispersion, adding to said dispersion, in suflicient amount to coagulate said polymer, a water-soluble metal salt which will not form an insoluble salt with acid present in said dispersion, and washing said coagulated polymer with water.

5. The process of producing a vinyl chloridecontaining polymer having a high stability against thermal decomposition which comprises adding to an aqueous dispersion of a vinyl chloride-containing polymer taken from the group consisting of polyvinyl chloride, vinyl chloridefumaric ester copolymers, vinyl chloride-vinyl acetate copoiymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-vinyl cyanide copolymers, vinyl chloride-acrylic ester copolymare, and vinyl chloride-methacrylic ester copolymers, said polymer containing at least 50%, by weight, vinyl chloride units and containing as the dispersing means therein a dispersing agent which is stable at a pH below 2.0, sufficient water-soluble acid taken from the group consisting of hydrochloric acid, sulfuric acid, acetic acid, and para-toluene sulionic acid to lower the pH value of the dispersion to less than 2.0 but insuflicient to coagulate the polymer from the dispersion, adding to said dispersion, in suflicient amount to coagulate said polymer, a water-soluble aluminum salt, and washing said coagulated polymer with water. i

8. The process of producing a vinyl chloridecontaining polymer, having a high stability against thermal decomposition which comprises adding to an aqueous dispersion of a vinyl chlors ride-containing polymer taken from the group mam 7 consisting oi polyvinyl chloride. vinyl-chlorideiumsric ester copolymers, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolylners, vinyl chloride-vinyl cyanide copolymers. vinyl chloride-acrylic ester copolymers, and vinyl chloride-methacrylic ester copolymers, said polymer containing at least 60%, by weight, vinyl chloride units and containing as the dispersing means therein a dispersing agent which is stable at a pH below 2.0, sufllcient watersoluble acid taken from the sroup consisting of hydrochloric acid, sulfuric acid, acetic acid, and

para-toluene sulionic acid to lower the pH value the dispersion to less than 2.0 but insumcient to coagulate the polymer from the dispersion, adding to said dispersion, in suiilcient amount to coagulate said polymer, aluminum sulfate and washing said coagulated polymer with water.

'I. The process of producing a vinyl chloride: containing polymer, having a high stability against thermal decomposition which comprises adding to an aqueous dispersion oi a vinyl chloride-containing polymer taken from the group consisting oi polyvinyl chloride. vinyl chlorideiumaric ester copolymers, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-vinyl cyanide oopolymers, vinyl chloride-acrylic ester copolymers, and vinyl chloride-methacrylic ester copolymers, said polymer containing at least 50%, by weight, vinyl chloride units and containing as the dispersing means therein a dispersing agent which is stable at a pH below 2.0, sumcient hydrochloric acid to lower the pH value oi the dispersion to less than 2.0 but insumcient to coagulate the polymer irom the dispersion, adding to said dispersion, in suiilclsnt amount to coagulate said polymer, a water-soluble aluminum salt and washing said coagulatcd polymer with water.

8. The process of producing a vinyl chloridecontaining polymer, having a high stability :glaiflnnst thermal decomposition which comprises sumcient amount to coagulate said polymer, aluminum suliate, and washing said coagulated polymer with water.

v. WILLIAMB.

REFERENCES crrnn The i'ollowing'reierences are of record in the tile or this patent:

UNITED STATES PATENTS Number Name Date 2,882,012 Parker Aug. 14, 1945 0 2,392,758 Mighton June 8, 1948 2,419,122 Cox Apr. 15, 1947 copolymers, vinyl chlo- 

